Bonobo communities have ranges that overlap with other groups. Males are protective of other members of their group and carry out any hunting. Males typically remain among their family group while females range further afield. While males show aggression towards each other, conflict rarely escalates into acts of physical violence. In spite of physical superiority, evidence suggests that males are not aggressive towards females. Bonobos are social animals, and food sharing occurs between males and females, unlike the situation with chimpanzees. Also the female–female relationship is much stronger in this species than it is for chimpanzees. Although they seem very lively, bonobos, like humans, control their emotions when expressing themselves in times of happiness, sorrow, excitement or anger. They are very animated and perform similar gestures to humans when communicating without using language. For example, they will beg by stretching out an open hand or foot and will make a whimpering sound if they fail at something. Females become sexually mature after about twelve years of age and may give birth soon thereafter. They have babies at five- to six-year intervals, so population growth can never be rapid. As with humans, there is a relatively long period of socialization for the young. Females nurse and carry their babies for five years, and the offspring reach adolescence by the age of seven. Females have between five and six offspring in a lifetime.
ACTIVITY
Make a list of the differences and similarities between humans, bonobos and chimpanzees. Are there more similarities or more differences?
Tool-use
Tool-use was once thought to be one of the characteristics that set humans apart from other primates, and, indeed, if you look at the variety and complexity of the tools employed by humans, this would seem to be true. However, tool-use has been seen in a number of primate and nonprimate species, both in captivity and in the wild. The study of tool-use provides important information concerning the evolution of human abilities.
A tool can be defined as any object manipulated by an animal in order to perform a specific task. This tool usually has some beneficial effect, such as making a task easier. Therefore, a tool can be very simple, such as a stick to scratch the animal’s back. This sort of tool, which requires no alteration to be functional, is sometimes described as a ‘naturefact’. Tools used by nonhuman primates include stones, which might be used to cut, grind or scrape.
Chimpanzees, for example, often make use of tools. They will adapt sticks, rocks, grass and leaves and use them when foraging for honey, termites, ants, nuts and water. Despite the lack of complexity, there does seem to be planning and skill involved in using these tools. For example, when foraging, chimps will employ modified short sticks to scoop honey out of a hive – that is, if the bees are harmless. With the hives of the dangerous African honeybee, they use longer and thinner sticks to extract the honey. Modification of leaves and branches, and their use as simple tools, has also been observed in elephants, crows and dolphins. However, none of those species created or used more sophisticated tools, such as the stone tools that earlier hominins started to produce more than 2 million years ago. Human tools of course became much more complex and diverse: hunting tools, tools to create and control fire, and much more.
Bipedalism
Modern chimpanzees occasionally walk upright, but their skeletons are not adapted for regular walking on two legs. The skeletons of early humans, on the other hand, evolved to support their bodies in an upright position. This means that modern humans have bodies adapted for walking and running long distances on two legs – that is, they are bipedal. Walking upright undoubtedly helped early humans survive in the diverse habitats in which they lived, including forests and grasslands. There are several physical changes that had to occur to make bipedalism possible, among them modifications in foot and knee structure, a curved spine (to absorb shock), broad-shaped hip bones, and a change in the point of attachment between the skull and the neck from a posterior position (as found in other primates) to an inferior position. Bipedalism was an adaptation to the open environments of the African savannah, where the earliest hominins evolved.
bipedalism Walking upright on two feet for the majority of time
One disadvantage of bipedalism is that climbing is much harder, as the feet cannot grip trees. Another disadvantage is the back pain and other skeletal problems that occur as a result of walking upright. Placing all the body’s weight on just two limbs can result in back pain and slipped discs. A further disadvantage of bipedalism was that it resulted in the narrowing of the hips and pelvis, resulting in greater risk in childbirth.
Human pelvis shape and size are different from those of other primates
As we have seen, bipedalism and the long, slim bodies that go with it were advantageous for humans to be able to move quickly and efficiently in the savannah environment. However, these changes also resulted in changes in the shape, size and position of the female pelvis, which meant a narrower birth canal in females. As a consequence, giving birth became a more difficult and risky process for humans than for most other primate species. The result is that humans give birth to babies that have not achieved the stage of brain development that is typical at birth for apes, monkeys and most other mammals. This particular feature of our evolution appears to be quite recent; it was around 500,000 years ago that there was evidence of the large human brain.
mammal Any warm-blooded vertebrate animal, including humans, characterized by a covering of hair on the skin and, in the female, milk-producing mammary glands for feeding the young
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